It said in one statement that its IT team has worked continuously to restore access to three main clinical systems. It said no patient data or associate data was compromised.

Ransomware has become one of the most prevalent kinds of malware on the Internet although it has been around for more than a decade.

Several medical facilities have come forward over the last few weeks and publicly said ransomware had disrupted their operations. The targeting of medical groups has added a new and dangerous angle to these kinds of cyberattacks because patient care could be directly impacted.

MedStar encouraged patients on Wednesday to call doctor offices directly to make appointments, as it was still trying to restore its electronic appointment system.

Nonetheless, MedStar said it has been able to keep humming along. Since the attack, it has cared for 3,380 patients a day across 10 hospitals, performed 782 surgeries and delivered 72 babies.

"The malicious malware attack has created many inconveniences and operational challenges for our patients and associates," according to a statement. "With only a few exceptions, we have continued to provide care approximating our normal volume levels."

The Baltimore Sun reported the hackers offered MedStar a bulk decryption discount: three bitcoins to decrypt one computer, or 45 bitcoins, roughly US$18,500, to unlock them all.

That demand is roughly in line with the attackers who struck Hollywood Presbyterian Medical Center in Los Angeles. Allen Stefanek, president and CEO of Hollywood Presbyterian, said in a statement the payment was the "quickest and most efficient way" to restore its systems.

The ransom note and the Tor hidden website supplied to make a payment was "almost identical" to those who have previously been infected with ransomware called Samsam, the Sun reported.

Just days before MedStar announced its troubles, Cisco's Talos group published a blog post on Samsam, which is also called Samas and MSIL.B/C.

Craig Williams, Cisco's security outreach manager, wrote "this particular family seems to be distributed via compromising servers and using them as a foothold to move laterally through the network to compromise additional machines which are then held for ransom. A particular focus appears to have been placed on the healthcare industry."

Samsam's operators were using JexBoss, a penetration testing tool for JBoss servers, to get access to networks, Williams wrote.

It's unclear how MedStar has been able to restore its systems. But computer security experts closely analyze ransomware and have occasionally been able to find errors in the code that would allow the recovery of the decryption key.

Authorities are largely at a loss for how to stop ransomware. Some of the ransomware gangs, believed to be in Eastern Europe or Russia, are far out of the reach of law enforcement.

Companies and organizations have generally been advised to frequently back up their systems and ensure those systems are segregated to prevent ransomware from encrypting those files as well. But designing such systems is not easy, and small organizations with less to spend on IT may be more vulnerable.

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